This invention relates to an improvement in safety circuits for cleaning lances which utilize high pressure water, and which require a pair of trigger circuits to be held closed in order to direct the water against the surface to be cleaned.
In the prior art, high pressure water is often utilized to clean surfaces. As an example, paint, dirt and other sludge may be removed from a surface by jetting high pressure water out of a hand-held cleaning lance. Typically, the cleaning lances are provided with triggers which must be held closed in order for the high pressure fluid to be directed outwardly of the lance. If the trigger is released, then a mechanical connection within the lance moves to open a dump valve, and direct the high pressure water to a dump outlet at which it is allowed to leave the lance at a reduced pressure.
The trigger ensures the high pressure water is stopped when cleaning is to be interrupted, and also provides a safety benefit in that the lance must be held in the hand of a user with the trigger closed for the high pressure water to be directed outwardly of the lance. This reduces the likelihood of high pressure water being directed in undesired directions if the lance were dropped.
More recently, there have been two innovations to this type of cleaning lance. In a first innovation, a pair of triggers are provided on the lance. The two trigger lances require the operator to have the lance firmly held in two hands, with both triggers closed. If either trigger is opened, then the valve opens. An example prior two trigger lance is shown in U.S. Pat. No. 5,904,297, which is owned by the assignee of the present invention.
One other recent innovation is the replacement of the mechanical connection with electric trigger switches. A control monitors whether the trigger switches are closed, and opens the dump valve should a trigger switch be released. The electronics necessary for the operation of such a valve are known in this art.
One problem with the above-discussed two trigger devices is that users have sometimes tried to circumvent the “double” trigger safety function. In the past, users have been known to tape one of the triggers closed such that the lance need not be held in both hands firmly. This obviously defeats the purpose of the two-switch safety device.